People buy me to eat, But Never eat me what m I?

answer is b,

"the tracer looks harmless in flight, but the pilot’s bitten lips and white knuckles suggest how dangerous it can be."

it was correct.

the gas pressure p, gas volume v, and gas temperature t are given in the formula:   pv=nrt,

r is the gas constant, and n is the number of gas moles.

if the container is cooled and remains under atmospheric pressure, where r is a constant that does not change, the volume of the container remains the same, the conclusion is drawn that, with all other values ​​unchanged, the number of gas moles n, is decreases.

the right answer is a.